Analysis of biomedical time series plays a key role in clinical management and basic investigation. However, most conventional monitors streaming data in real-time show only the most recent values, not referenced to past dynamics. The proposed visualization method (termed “data chromatix”) was developed to address this challenge by bringing memory of the system’s past behavior into the current display window.

The function DataChromatix.m (version 1.0) assigns a color to each data point of a time series. The color is determined by the values of a normalized histogram (estimated probability density function) computed from a pre-selected segment of the data. The algorithm receives the time series as input and generates a video of its colorized version as it would look on a typical monitor display, as well as a static graph of the entire colorized signal.

The algorithm has the following parameters: the memory and colorization window lengths, the shift (s), the histogram bin size, and the number of colors (c) in the chromatic map (Fig. 1).

Figure 1: Memory window and colorization window at a given time tC and at the following time instant tC+s. Both windows are shifted to the right by the shift s. Adapted from (1).

At each step, a normalized histogram of the data points in the memory window is computed. Then, the interval [0,1] is divided into c adjacent intervals, and each interval is assigned a color. If the jet color-map is used, the interval [0,1/c) corresponds to dark red and the interval ((c-1)/c,1] corresponds to dark blue. Subsequently, each data point in the colorization window is assigned the color of the histogram bin into which it falls. Finally, the colorization window is advanced by the shift, s, and the memory window is either extended or advanced by the same amount (Fig. 2).

Figure 2: Schematic illustration of the colorization algorithm: the histogram of the time series (left panel) is colorized according to the bins height. Each point of the time series (right panel) is then colorized according to the bin it belongs to. Adapted from (1).

This colorization algorithm is intended to facilitate analysis of physiologic and non-physiologic time series. Future studies will help assess its utility.